1. The Field of the Invention.
The field of the invention relates to an improved electronic sewing machine, more particularly of the type in which the needle bar is driven by solenoids.
2. Description of the Prior Art.
Electromagnetic force has been utilized to operate needle bars in sewing machines. Reference is made to U.S. Pat. No. 2,232,692 (Feb. 25, 1941 to Diehl); U.S. Pat. No. 3,425,376 (Feb. 4, 1969 to Brynge, et. al.); U.S. Pat. No. 3,831,537 (Aug. 27, 1974 to Siegel); U.S. Pat. No. 3,881,433 (May 6, 1975 to Davidson); U.S. Pat. No. 4,098,207 (Jul. 4, 1978 to Peterson). Each recognizes that utilization of solenoids and magnetic fields will reduce friction in a sewing machine which is generally dependent on a mechanical transmission with many moving parts. None, however, avoids the fact that somewhere in the driven train an ordinary electric motor is essential to operate a portion of the particular configuration disclosed and more specifically to operate the bobbin.
Of interest is Brynge, et. al. in which the needle bar is reciprocated by changes in the magnetic flux of a permanent magnetic field induced by a movable iron-free driving coil which is synchronized with the bobbin or loop taker. The bobbin is independently driven by a variable speed, rotating electric motor which generates pulses to the drive coil and regulates the stitch rate from a zero to a maximum. The motor itself typically has a magnet bearing wheel which will generate one pulse per wheel rotation as the bobbin is driven through one cycle.
Nowhere in any of the devices referred above nor otherwise presently known to your inventors is a true stepping motor utilized to control stitch cycle and stitch tightness or quality nor of a solenoid-driven sewing machine of such a configuration as to be maximally free of many or continuously moving parts. None is responsive to instructions from a central processing unit for controlling the sewing cycle and each is, as a result, inflexible as to operation except in the variation of the stitch rate.
As is well known in the art, stitch tightness is regulated by repositioning the bobbin assembly's rotation, conventionally by a manually adjustable screw. A variation in sewing together a number of plies or thickness of material, for example, requiring in the middle of a sewing operation, or sewing a thicker elastic material to a lighter non-elastic kind, will cause uneven stitching and might require a manual readjustment to the bobbin assembly to accommodate the change. In and of itself, such uneven stitching could cause rejection by an inspector.
Except for Brynge, each in its operation requires some kind of continuously running drive and clutch arrangement and is therefore energy inefficient. Brynge, as a limitation, does not provide electronic means for regulating stitch quality. Further, the foregoing prior art, or existing apparatus of the type known to your inventors apparatus of the type, provides a way of controlling stitch or run of stitch counts, such prior art in the disclosure is operator dependent for such purposes.
Reference is also made to U.S. application Ser. No. 07/508,221 (Frankel) filed Apr. 17, 1990 now pending an allowed which contains some related subject matter. However, it is not cited as containing prior art.